This invention is directed to a waterbased coating composition and in particular to a waterbased coating containing a methylol (meth)acrylamide acrylic polymer, a polyurethane and an alkylated melamine crosslinking agent.
Methylol (meth)acrylamide acrylic polymers are polymers containing polymerized monomers of methylol methacrylamide or methylol acrylamide or any mixtures thereof.
Waterbased coating compositions useful for base coats and clear coats for automotive applications are shown in Wilfinger et al U.S. Pat. No. 4,730,020, issued Mar. 8, 1988. Waterbased dispersions of polyurethane are known as shown in Drexler et al U.S. Pat. No. 4,489,135, issued Dec. 18, 1984. Processes for preparing aqueous dispersions of acrylic polyesters are shown in Osborn et al U.S. Pat. No. 3,925,295 issued Dec. 9, 1975 and Osmond et al U.S. Pat. No. 3,935,155 issued Jan. 27, 1976. However, none of the compositions shown in the art form finishes having properties that are required in particular for exterior finishes of automobiles and trucks.
To date, solvent based paints have been the predominant finishes used to coat the exterior of automobiles and trucks. These solvent based paints have excellent adhesion to the substrate and provide properties such as weatherability, gloss, hardness, distinctness of image that are required for the finishes of the exterior of automobiles and trucks. To meet desired standards of reduced solvent emissions and achieve lower baking temperatures to save energy, waterbased paints were suggested for use. However, none of the known water based paints form finishes that have the necessary properties for automotive and truck use along with lower baking temperatures.